Communifire - Enterprise Social Collaboration Software
Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
DigitalChalk - Online Training Software and Learning Management System (LMS)
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
Workplace by Facebook - Connect everyone in your company and turn ideas into action.
Sipdroid - Free and open-source SIP/VoIP Client